rio de janeiro -25-28 august 2014 ultimate energy ......aug 28, 2014 · wasteeng 2014 rio de...

WastEEng 2014Rio de Janeiro - 25-28 August 2014

Ultimate energy performances ofgrate combustor WtE plants

S. Consonni, F. Viganò, E. BogaleDepartment of Energy, Politecnico di Milano

2The paths of energy recovery from waste

RDF

Com

bust

ion

Piro

lysi

s

MSW

Com

bust

ion

Com

bust

ion

RDF

mec

hani

cal

trea

tmen

t

Synthetic fuels:H2, liquid fuels

Gas

ifica

tion

bio-

dige

stio

n in

land

fill

Gas

ifica

tion

Focus of this presentation:

S. Consonni - WastEEng 2014, 28 Aug 2014

Syngas - Biogas

+ Heat

Electricity

Com

bust

ion

gas

turb

ine,

int.

com

bust

ion

engi

ne

stea

mcy

cle

Com

bust

ion

Com

bust

ion

Com

bu-

stio

n

pressurized steam

presentation:

gratecombustors with production of electricity only

33Basic issues of Energy from Waste: a reminder

• Unfavourable physical properties (solid chunks) --> grate, long residence times, large combustion chamber

• Unfavourable composition:

− high moisture content --> low boiler efficiency

− high ash content --> high aux power consumption, erosion, large boiler


− corrosive species --> limit steam conditions

− pollutants --> heavy flue gas treatment

• Heating value much lower than for fossil fuels --> for given power, large flow rates --> high aux power consumption, high costs

• Small scale --> low efficiency, high costs

4The price to pay for low quality waste fuel

Eur

o/kW

el

0

2,000

4,000

6,000

8,000

10,000

1 2 3

WTE plant WTE plant

Capital cost

As a consequence of extremely high capital costs and low efficiency, energy production


10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

1 2 3

Net

effi

cien

cy, %

WTE plant100.000 tons/yr

7.5 MWel,net

WTE plant1.000.000 tons/yr

100 MWel,net

Coal-fired plant1.000 MWel,net

Net electric efficiency

efficiency, energy production from waste is economically acceptable only for negative fuel prices (gate fee)

55

Although the competition with fossil fuel-fired power plants is extremely challenging (and somewhat unfair), viewing WTE plants as power stationspower stations rather than a disposal technology is the only way WTE can be accepted by legislators and the public opinion

Relevance of energy recovery


accepted by legislators and the public opinion

Waste = Resource

6Directions for improvement

1) Decrease costs– simpler configuration– use less material– ease/decrease maintenance– etc.

2) Increase efficiency– improve thermodynamic cycle


– improve thermodynamic cycle– adopt different combustion technology (fluidized bed ?)– adopt technologies other than combustion (gasification ?)

3) Generate additional ouputs– cogeneration of heat & power– recover materials from bottom ashes– etc.

7

400

500

600

700

kg C

O2

per

ton

of R

esid

ula

Was

te

Al recoveryFe recovery

Power stationFuel cycle

Emissions avoided

TransportAsh treatmentReagentsPlant constructionRW combustion

Emissions generated

Why efficiency is so important ?

Additional emissions of landfill 180 kg CO 2eq


5% 10% 15% 20% 25% 30%0

100

200

300

kg C

O2

per

ton

of R

esid

ula

Was

te

Net efficiency of WtE plant

Emissions generated net of landfill

"Break-even" efficiency ~ 15%

88

Performances achievable by state-of-the-art

Technologies


by state-of-the-artgrate combustors

99Modern, advanced combustion plant

STACK

EVA

ECO

FGR

WASTE

STEAM DRUM

SH

CONDENSATE PREHEATEREPS SCR

FABRIC FILTER

ASH ASH

EVA

FGR FAN

ASH


DEAERATOR FWH

PRIMARYAIR AIR PREHEATERS

GRATE FURNACE

BOTTOMASH VAPOR FROM

ASH QUENCHING

SECONDARY AIR

ASH

ASH

10Methodology of performance predictions

out

in

in

in

in 2

in1

out

out

fuel

out

out 2

in leakage

gas turbine coolingflows

IntercooledCompressor

Splitter

Mixer

Pump

Heat exchanger

in ex 2

out

outin1

in 2

Cooling air

in2

in1out 1

out 2

in1

in2

out 2

Saturator

W outW in

out 1

out 1

in

leakage

gas turbine coolingflows

Compressor

in (coolingfluid)

2

• GS modular code developed at PoliMI / Princeton

• Thermoflex / SteamPro

• Aspen Plus


fuel

Turbine Combustor

HRSG

Chemical converter

Oxygen separation plant

Shaft and generator

Exhaust gasAir

OxygenNitrogen

Qout

W in

inout

fue l airExhaust

ga s

SOFC

turbine inlet

toreheat

fromreheat

in out

outin out

feedwaterto boiler

Steam cycle

• estimation of operating parameters (P, T, mass flows) and performances of each component

• evaluation of mass / energy balances

• overall performances

• costs

11Typical operating parameters

small(conservative

design)

large(advanced

design)evaporation pressure 45 70extraction for air pre-heating 3.0 1.0/6.5 deaerator pressurecondensation pressure 0.10 0.06gas temperature at SH inlet

plant size

design parameter unit

bar2-3

max 650


gas temperature at SH inletsteam temperature at SH outlet 400 450gas temperature at end of heat recovery 160 135temperature of primary air 120 150temperature of secondary air 120 150

1 21 2

MP feedwater heatersflue gas recirculated % massoxygen at boiler outlet % vol 6.0 5.0loss due to unburnt carbon % LHV

°C

max 650

steam bleeds for air heaters

none15.0

0.8

LP feedwater heaters ahead of deaerator

1212Effect of steam parameters and scale

26

28

30

320 39 77 116 154 193 231 270 309

722

778

833

889

combustion power, MWt

advanceddesign

net e

lect

ric e

ffici

ency

, %

net e

lect

ric k

Wh

per

ton

of w

asteadvanced design

Pev 70 barTSH 450°C, etc.


0 100 200 300 400 500 600 700 80016

18

20

22

24

MSW treatment capacity, 1000 t/y

500

556

611

667

net electric kWh per ton of M

SW

conservativedesign MSW LHV

10 MJ/kg

net e

lect

ric e

ffici

ency

, %

LHV10 MJ/kg ne

t ele

ctric

kW

h pe

r to

n of

was

te

conservative designPev 45 barTSH 400°C, etc.

13

79

81

83

85

87

Ren

dim

ento

iso

entr

opic

o T

V [

%]

Isentropic efficiency of steam turbines

7800 RPM

4300 RPM

10400 RPM

Isen

trop

ic e

ffici

ency

of S

T [%

]


69

71

73

75

77

79

0 20 40 60 80 100 120

Potenza elettrica lorda [MW]

Ren

dim

ento

iso

entr

opic

o T

V [

%]

13

4300 RPM

6000 RPM

9000 RPM

11300 RPM

pIN = 65 barTIN = 450°Cpcond = 0.09 bar

3000 RPM12000 RPM

Isen

trop

ic e

ffici

ency

of S

T [%

]

Gross electric power [MW]

1414Industrial practice vs scale

26

28

30

32

rend

imen

to e

lettr

ico,

%

0 39 77 116 154 193 231 270 309

722

778

833

889

potenza di combustione, MWt

elet

tric

ità n

etta

, kW

h pe

r to

nn d

i RU

R

parametri avanzati

realtà industriale

Combustion power, MW LHV

Net

ele

ctric

effi

cien

cy, %

LHV

Net

ele

ctric

ity p

rodu

ctio

n, k

Wh/

tU

RW

Advanced parameters

Industrial practice

How can we shiftthis line upward ?


0 100 200 300 400 500 600 700 80016

18

20

22

24

capacità di trattamento RUR, 1000 t/y

rend

imen

to e

lettr

ico,

%

500

556

611

667

elet

tric

ità n

etta

, kW

h pe

r to

nn d

i RU

R

parametri conservativi PCI

10 MJ/kg

realtà industriale

Net

ele

ctric

effi

cien

cy, %

URW treatment capacity, 1000 t/y

Net

ele

ctric

ity p

rodu

ctio

n, k

Wh/

t

Conservativeparameters LHV

10 MJ/kg

Industrial practice

1515Possible routes to increase efficiency

1) Increase scale --> larger plants

2) Use auxiliary, high-quality fuels in complex, integrated configurations --> see presentation by dr. S. Guerreiro + related refs

3) Improve steam cycle:

− better cycle parameters --> higher Pev, TSH, lower Pcond

− more sophisticated configuration --> reheat


− more sophisticated configuration --> reheat

and given that:

• Pcond is determined by ambient conditions and water availability

• Higher Pev necessarily requires either higher TSH or reheat to limit liquid fraction at steam turbine outlet

• must go to either higher TSH and/or reheat

1616

Increase TSH ?

Routes to increase efficiency


Increase TSH ?

1717The challenge of higher TSH


Superheater tubes of plant in Acerra (Italy)

TSH = 500°C

1818

STACK

EVA

ECO

FGR

WASTE

STEAM DRUM

SH1


FABRIC FILTER

ASH ASH

EVA

FGR FAN

ASH

"Bypass" concept (Hans, 2010)


DEAERATOR FWH


GRATE FURNACE

SECONDARY AIR

SH2

COMBUSTOR

AIR

FUEL GAS

> 1λ λ

> 1λ

<1 GASCLEANING

1919

STACK

EVA

ECO

FGR

WASTE

STEAM DRUM

SH1


FABRIC FILTER

ASH ASH

EVA

FGR FAN

ASH

"Steam Boost" concept (Madsen, 2007)


DEAERATOR FWH


SECONDARY AIR

COO2

Cl

Na Zn

Pb

H O2 CO,CO

2

CH4,CXHY

CO,H2

STEAMBOOST SUPERHEATER

NON CORROSIVE GASES

WATERCOOLED MEMEBRANE WALL

GRATECOMBUSTOR

VAPOR FROMBOTTOM ASH QUENCH

2020External superheating with Biogas

STACK

EVA

ECO

FGR

WASTE

STEAM DRUM

SH1


FABRIC FILTER

ASH ASH

EVA

FGR FAN

ASH


DEAERATOR FWH


GRATE FURNACE

BOTTOMASH

SECONDARY AIR

ASH

COMBUSTOR

SH2

TO STACK

APH

BIOGASANAEROBIC DIGESTOR

AIR

2121

Given the challenge of high TSH, improving efficiency by adopting more sophisticated configurations - rather than by increasing TSH -seems attractive

Routes to increase efficiency


steam Reheat (RH)

2222Reheat via high-pressure liquid (Amsterdam)


2323Fisia-Babcock plant in Ruedersdorf (Berlin)


2424"Full" steam reheat

STACK

EVA

ECO

FGR

WASTE

EVA

ASH

STEAMDRUM

SH

RH

CONDENSATE PREHEATER

SCR

FABRIC FILTER

ASH ASH

SECONDARYAIR

EPS

EVA

FGR FAN


DEAERATOR FWH

PRIMARYAIR

AIR PREHEATERS

ASH

GRATEFURNACE


ASHQUENCHING

ASH

2525Assumptions

CONV RH130 RH150 RH170LHV of waste fuel MJ/kgcombustion power MWevaporation pressure 70 130 150 170reheat pressure - 25 25 25extraction for air pre-heatingdeaerator pressurecondensation pressuregas temperature at SH inletsteam temperature at SH outletsteam temperature at RH outlet - 450 450 450

450

3.00.07

max 650

design parameter unit

bar

plant configuration

10,34200

0.88/6.30


steam temperature at RH outlet - 450 450 450gas temperature at eco outletgas temperature at end of heat recoverytemperature of prim/sec air

blowdownwater ∆P/P in economizersteam ∆P/P in SH / RHflue gas recirculated (*) % mass 15.0 26.9 31.2 35.8oxygen at boiler outlet % voloxygen at stack % volunburnt carbon in bottom ash % massthermal losses in boiler / heat exchangers %

(*) as fraction of flue gas flow at economizer outlet

1.0

6.07.0

190135150

15.08.0

1.0

2.0

%

LP feedwater heaters ahead of deaerator22

°C

steam bleeds for air heaters

2626Thermodynamic cycle

70 bar

130 bar

170 bar150 bar

Reheating 170 bar

Reheating 150 bar

Reheating 130 bar

Tem

pera

ture

(°

C)


0.07 bar

25 bar

Conventional

70 bar

Tem

pera

ture

(

Entropy (kJ/kgK)

2727Implications for boiler design

Conventional plant, Pev=70 bar, TSH=450°C, FGR=15%

Tgrate=1141°C T at inlet of convective section 650°C

flue gaseswater/steam


2828Implications for boiler design

Plant with RH, Pev=170 bar, TSH=TRH=450°C, FGR=15%

T at inlet of convective section 694°C

Tgrate=1141°C



2929Higher FGR as means to mitigate Tgas

T at inlet of convective section 650°CTgrate=1060°C

Plant with RH, Pev=170 bar, TSH=TRH=450°C, FGR=22.9%



3030"Flue Gas Quench" (FGQ)

STACK

EVA

ECO

FGR

WASTE

EVA

ASH

STEAMDRUM

SH

RH

CONDENSATE PREHEATER

SCR

FABRIC FILTER

ASH ASH

SECONDARYAIR

EPS

EVA

FGR FAN

gas quench


DEAERATOR FWH

PRIMARYAIR

AIR PREHEATERS

ASH

GRATEFURNACE


ASHQUENCHING

ASH

3131"Flue Gas Quench" (FGQ)

Plant with RH, Pev=170 bar, TSH=TRH=450°C

FGR = 15%(*) in comb. chamber+FGR = 7.9%(*) at outlet of radiative section

gas quench



section

(*) referred to flow at outlet of economizer

3232

CONV RH130 RH150 RH170combustion power MW

evaporation pressure 70 130 150 170reheat pressure - 25 25 25condensation pressure

steam temperature at SH outletsteam temperature at RH outlet - 450 450 450

gas temperature at exit of radiative section 650 673 688 694

gas temperature at inlet of convective section 650 650 650 650

Flue gas generated on the grate 124.4 124.4 124.4 124.4

plant configuration

200

0.07450

°CAss

umpt

ions

design parameter

°C

unit

bar

Main results: conventional vs RH with FGQ


Flue gas generated on the grate 124.4 124.4 124.4 124.4

FGR to combustion chamber 21.9 21.9 21.9 21.9

FGR to quench at exit of radiative section 0.0 7.6 12.7 15.0

Flue gas in convective section 146.3 153.9 159.0 161.3

FGR, kg per kg at boiler outlet 15.0 19.2 21.8 22.9

FGR, kg per kg generated on the grate 17.6 23.8 27.8 29.7

Steam at HP turbine inlet kg/s 66.04 60.45 60.55 60.65

Gross power HP turbine - 16.71 18.09 19.43Gross power LP turbine - 54.09 56.44 57.67

Total gross power 63.51 70.80 73.60 77.10

Net Power 56.38 63.53 66.26 69.70

Net extra power generated with RH, FGQ - 7.15 9.88 13.32

Gross Electric Efficiency 31.75 35.40 36.80 38.55Net Electric Efficiency 28.19 31.76 33.13 34.85

MWel

kg/s

Res

ults %

%

3333Efficiency vs Pev

30

32

34

36

Net

effi

cien

cy, %

reheat,


40 60 80 100 120 140 160 180

Evaporation pressure

24

26

28

30

Net

effi

cien

cy, %

conventional

reheat,flue gas quench

3434Capital costs (Euro 2014)

• Base estimate carried out with SteamPro / PEACE

• RH cases corrected for extended Inconel cladding + refractory coverage:

– 100% of radiative section covered with refractory (1100 Euro/m2) or Inconel (3400 Euro/m2)

– evaporator + high-temperature SH and RH (for a total of about 25% of total surface of convective section) completely


about 25% of total surface of convective section) completely covered with Inconel (2500 Euro/m2)

• Additional corrections to SteamPro/PEACE predictions for Electric systems, solid handling, buildings and civil works based on experience of major WTE built in Italy in the last decade

NOTICE: cost of convective sectionconvective section of boiler increases very substantially, but cost of radiative sectionradiative section tends to decrease (lower thermal power, smaller tubes)

3535Capital costs (Flue Gas Quench, Euro 2014)

Evaporation pressure, bar 70 130 150 170

Gross power output, MWel 63.51 70.80 73.60 77.10

RH No Yes Yes Yes

Grate Combustor + Boiler 106,023,271 142,650,594 147,874,391 147,993,662

Flue gas treatment system 25,659,239 27,817,262 28,818,427 32,359,935

Steam Turbine 11,049,716 14,916,068 15,624,692 16,177,916

Heat rejection system 2,726,335 2,667,227 2,720,810 2,788,220

Other components of steam cycle 1,213,331 1,272,090 1,190,703 1,386,017

Electric system + transforms + DCS 7,659,061 8,309,219 8,554,490 8,857,999


Waste handling 3,177,930 3,177,930 3,177,930 3,177,930

Handling of solid residues 2,398,599 2,398,599 2,398,599 2,398,599

HVAC+Buildings 11,938,833 11,938,833 11,938,833 11,938,833

Balance of plant 1,337,969 1,342,847 1,353,852 1,375,690

Civil works, roads and construction 25,854,501 25,254,224 25,205,628 25,076,495

Mechanical works 76,418,032 65,640,222 62,291,223 58,480,012

Engineering and Plant startUp 9,780,023 11,144,403 11,197,343 11,224,896

Total plant and Civil costs 285,236,840 318,529,520 322,346,922 323,236,204

Contingencies 10% 28,523,684 31,852,952 32,234,692 32,323,620

Design, safety, testing, insurance, etc 7,5% 21,392,763 23,889,714 24,176,019 24,242,715

Grand Total 335,153,287 374,272,186 378,757,634 379,802,540

3636Back-of-the-envelope cost assessment

• Extra-power generation = 13.32 MW

• Extra electricity generated in 1 yr (7800 hrs) = 104 GWh

• Extra capital cost = 44.6 M€

Plant with RH, Pev=170 bar, TSH=TRH=450°C, Flue Gas Quench

PRELIMINARY, CONSERVATIVE ESTIMATE


• Extra capital cost = 44.6 M€

• Assume Capital Carrying Charge 15%

• Add 4% per year of investment for O&M

• Thus, extra costs = 44.6 M€ · 0.19 = 8.5 M€/yr

• Break-even value of electricity =

[8.5 M€/yr] / [104 GWh/yr] = 81.7 €/MWh

3737Conclusions

• Given the very unfavorable characteristics of the waste fuel, improving the performance of WTE plants poses extreme challenges

• For grate combustors plants fed only with waste, steam reheat seems an interesting option

• The introduction of RH calls for a comprehensive redesign a comprehensive redesign of the whole integrated boilerof the whole integrated boiler. Flue Gas Quench allows


of the whole integrated boilerof the whole integrated boiler. Flue Gas Quench allows limiting the size and the cost of the radiative section while keeping safe temperatures in the convective section

•• Preliminary, conservativePreliminary, conservative estimates show that with PEV=170 bar and Tmax of steam 450°C it is possible to increase net efficiency of over 6 percentage points6 percentage points

• For a 200 MWLHV plant, the extra electricity generated with RH comes at a cost in the neighborhood of 80 80 €€/MWh/MWh

3838

Thank you for your attention !

Conclusions


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rio de janeiro -25-28 august 2014 ultimate energy ......aug 28, 2014 · wasteeng 2014 rio de...

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