technoeconomical study of bio-sng production from...
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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
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• 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.