9.5.2011

Technoeconomical study of bio-SNG production from lignocellulosic biomass

EGATEC Conference 12-13.5.2011 GERG Network Researcher Kristian Melin Aalto University School Of Chemical Technology Bio and Chemical Technology

9.5.2011

• Different Lignocellulosic Biomass (Potential from a Finnish perspective)

• Transport from site to plant • Bio-SNG Conversion Technology

– Pre-Treatment for bio-SNG Production – Gasification – Synthesis gas Cleaning – Shift Reaction and Methanation

• Economics of bio-SNG production • Sensitivity Analysis • Effect of Plant Scale on Economics • Conclusions • Acknowledgement

Outline of presentation

9.5.2011

• Forest Chips – branches, stumps, and small wood. – logging residues per m3 of log usually 20-40 % which is used in paper and pulp industry. – Potential in Finland 23,5 TWh (Simola 2010) 0->40 m3/km2/y Ranta (2004) – Logging Residues mostly available followed by small wood and stumps.

• Agricultural Biomass – Reed 30 MWh from 1 ha, 1t ~4,5 MWh density very low 60-80m3 if not densified. – With 10% use of available farming land in Finland 6-9 TWh could be obtained annually. – Straw potential around 1 TWh and10 MWh/m3 Lötjönen (2007)

– Products from pulp and paper industry for example lignin separated from black liqour could be used.

Different Lignocellulostic Biomass

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Transport of biomass from site to plant

• Harvest of Energy Biomass from the forest. • Transport :

– Truck transport of biomass • The truck maximum weight in Finland for example 60t (40 t of load) and volume 145

m3. • Logging residues only compacted (volume limiting) • Logging residues as Felling logs. (mass limiting) • Chipped Biomass (mass limiting)

– rail transport . – by ship.

• Estimation of transport costs – Transport costs for logging residue as felling logs 2 € +0,07 x100 km for

biomass transport distance one way. – Assumed that the average transport distance equals radius of harvest area

. • For agricultural biomass (reed, wheat straw the transport of 40 km transport cost of

4 €/MWh have been reported.

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Pre-Treatment of biomass before gasification

• Requirements for gasification – Particle size:

• In Fluidized bed particle size up to 25-30 mm and chips tolerated Bridgwater(2002).

– Moisture Content: • Less than 15 w-%. • Heat released in the process can be utilized in drying of wet biomass with

flue gas, steam or low temperature air. • Torrified biomass with very low moisture (3 w-%) content be pulverized

and gasified as dust in entrained bed gasifiers.

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Gasification Technology – Oxygen and Steam

• Heat from combustion drive the endothermic gasification reactions.

– Indirect Gasification Using Steam • Two stage heat transfer agent and remaining charcoal from gasification are separated and combusted with air heating the sand (heat transfer agent). • In the second stage steam is added and required heat is obtained from the

hot sand.

– Hydrogasification • Hydrogen reacts with carbon in an exothermic way giving methane with

high yield. • The gasification reaction is slower than with steam or CO2.

– Supercritical Gasification (at critical conditions of water). – Gasifier types: Bubbling fluidized Bed and Circulation Fluidized Bed.

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Synthesis gas clean-up – For bio-SNG synthesis the raw synthesis gas needs to be cleaned from following impurities.

• Tars can be destroyed by catalytic cracking using dolomite or Nickel catalyst or thermally by adding oxygen to the gas so that temperature is increased to <1000°C. • Alkalis (Na and K)

– Exist in vapor phase at high temperatures are removed in wet scrubbing system or by adsorption.

• Chlorine – Can be removed by adsorption or water scrubbing etc.

• Sulphure – Can be removed by scrubbing using an physical solvents, amines etc. – removed somewhat by dolomite – Low levels can be removed by ZnO beds.

• Nitrogen (NH3 and HCN) – Ammonia readily dissolves in water can be removed by scrubbing. – HCN can be hydrolysed into NH3 .

• Particulates – Fine particles not removed by cyclone can be removed with ceramic filters.

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Shift reactor – If methanation catalyst do not have water gas shift activity a separate shift reaction stage might be needed. – High Temperature (300-500 ºC)Iron Chromium Oxide

– Low Temperature shift (º180-270) sensitive to sulphur.

– Raw Gas shift (200-500 ºC) cobalt and molybdenum catalyst can withstand high amount of sulphur etc.

Methanation – CO and CO2 reacts with H2 into CH4 and H2O while large amount of heat is released.

• Catalyst for example Nickel is sensitive to sulphur impurities in the gas. – Lower temperature and higher pressure favorable for methane production – Carbon formation problem especially at high pressure and low temperature – Fixed bed methanation,

• Many reactors with intermediate cooling or gas recycle operated at elevated pressures.

• Temperatures up to 650 ºC (Rostrup-Nielsen et al., 2007) can be used

– Fluidized bed reactors • Single reactor isothermal operation. • Can be operated around 300ºC even at atmospheric pressures.

Synthesis gas reaction to form bio-SNG

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Assumption for Techno-economic Calculation Process parameters

• Direct oxygen blown gasification with gasifier outlet temperature 800 °C • Biomass composition as ultimate composition of Spruce Biomass and

Lower Heating value as input and Biomass moisture content 15 w- % (assumed to be dried to by steam generated)

• Gas purification 2 MJ/Kg of removed CO2 • The yield of SNG estimated from gasifier outlet composition and reaction

stoikiometrics for the Shift and Methanation reactor. • Gas with H2/CO ratio 3 is produced and CO2 is removed before

methanation. • Eletricity consumption estimated for synthesis gas compression and

oxygen manfucturing ( 80 kWh ton of biomass). Economics

• Operation cost calculated based on simulation model • Investment cost taken from VTT:s estimate 200 milj euros for300 MW

SNG plant and scaled according to capacity and corrected from time McKeough (2005 )

Biomass Biomass Gasification

5 bar and 800 CCO-SHIFT H2/CO ratio 3

CO2 Separation

Steam

Gas Compression to 25 bar

Methanation at350 C HP steam produced in reactor cooling

Flash To Separate Water

SNG

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Economics of total bio-SNG Process Total Biomass Feed on LHV basis (MW) 300Efficiency to SNG on LHV basis % 67

Total electricity Consumption MW 13.2Heat for amine Regeration MW 38.4MP Steam Selling Price €/MWh 13Electricity Price €/MWh 40Annual operation h/a 8000Life Time of Invesment in years 20Required rate on the capital% 10

Production costs Milj €/a % of totalBiomass Transport 13.8 19.6Biomass 26.4 37.7Annuity of inv. Cost 26.6 37.9Electricity 4.2 6.0Steam ( income) -0.8 -1.1

70.1 100.0

Logisctics

Biomass at Collection site

Biomass Transport cost

by TruckBiomass at

Plant

Average Transport distance Yield

€/MWh €/MWh €/MWh km m3/a/km211 5.7 16.7 138 20

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Sensitivy analysis of bio-SNG production Sensitivity Analysis of bio-SNG Production

0

10

20

30

40

50

60

-60 -40 -20 0 20 40 60

Change on the variable in %

Prod

uctio

n co

st o

f bio

-SN

G (€

/MW

h)

Investment CostBiomass CostsTransport CostsSNG Yield

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Effect of plant scale on the economics

bio-SNG Production cost as function of Capacity

30

35

40

45

50

55

0 200 400 600 800 1000 1200 1400

Plant capacity Biomass Input [MW]

SNG

Pro

duct

ion

cost

[€/M

wh)

€/MWh

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Conclusions • The yield of SNG affects the production cost mostly of the studied variables. • The Investment cost and raw material effect the productions cost more whereas the transport cost

where less significant. • Indirect steam gasification has been reported more

economically feasible compared with direct oxygen gasification. • Hydrogasification combined with converting formed CO from

biomass into hydrogen should be studied more in detail due to high efficiency of hydrogasification.

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Thank You! • Special Thanks to:

– Colleagues at Plant Design: – Markku Hurme, Raja Mudassar and Jukka Koskinen. – Sari Siitonen at Gasum for kind invitation to GERG network and valuable cooperation. – Finnish Science academy: Concepts of 2nd generation biorefinery. – Walter Ahlström foundation for funding.