CHALLENGES in BIOMASS GASIFICATION
Transcript of CHALLENGES in BIOMASS GASIFICATION
www.ecn.nl
CHALLENGES in BIOMASS
GASIFICATION
Bram van der Drift
Regatec, Barcelona, 7-8 May 2015
ENERGY BALANCE gasification process (e.g. at 800°C)
Gas
ifie
r
Solid fuel (LHV)
Gaseous fuel (LHV)
Heat in gaseous fuel
Heat loss
Carbon loss (in ash)
100%
70-95%
10-20%
1-5%
0-20%
LHV: Lower Heating Value Excluding electric energy use of: pumps, fans, oxygen production (if any), … Excluding energy recycle: e.g. air preheat and tar recycle
Main target!
Useful
COMPOSITION biomass is much different from coal
Clean wood Waste wood Straw Coal RDF
water wt% wet 20-60% ~20% ~20% ~10% ~10%
C wt% daf 50.7% 50.5% 48.8% 79.2% 60-65%
H wt% daf 6.1% 5.9% 5.9% 5.3% 8-9%
O wt% daf 42.8% 42.6% 44.0% 13.5% 25-30%
N wt% daf 0.28% 0.73% 0.85% 1.53% ~0.5%
S wt% daf 0.06% 0.14% 0.14% 1.30% ~0.2%
Cl wt% daf 0.04% 0.09% 0.43% 0.14% ~1%
volatiles wt% daf 82% 81% 81% 42% 85-90%
HHV MJ/kg daf 20.1 20.2 19.3 31.8 27-29
ash wt% dry 1.6% 6% 7% 12% 10-15%
main ash components Ca Ca, Si, Fe K, Ca, Si Si, Al Al, Ca, Si
Wet/dry/daf: based on wet/dry/dry-and-ash-free mass RDF: Refuse Derived Fuel Waste wood: excluding particle board
Straw: wheat, rye, barley Coal: average Dutch coal plants Source: www.phyllis.nl
HEATING VALUE in combustion, differences disappear
0
1
2
3
0
10
20
30
40
50
60
methane coal ethanol wood
Low
er H
eati
ng
Val
ue
[MJ/
k g
fuel
/air
mix
]
Low
er H
eati
ng
Val
ue
[MJ/
k g
fuel
]
LHV [MJ/kg fuel] - left axis LHV [MJ/kg fuel/air mix] - right axis
VOLATILES biomass has high volatile content: ~80% daf
Good:
• “Instant gas”: Good conversion at already low residence time, low temperature, low steam
• Valuable hydrocarbons in the gas (methane, ethylene, BTX)
• That also means that efficiency is better
• High calorific gas
Bad:
• Quickly responding to changes in e.g. feed
• Carbon remaining is porous and reactive: spontaneous ignition
• Tars
This presentation focuses on fluidized bed processes: 700-900°C
HYDROCARBONS modest in volume, but dominating in energy
“instant” natural gas: efficiency benefit
Ind
irec
t fl
uid
ized
bed
ga
sifi
cati
on
(M
ILEN
A)
of
wo
od
~8
00
°C
sometimes challenges, but certainly opportunities
METHANE CONTENT is BENEFIT efficiency from biomass to bioSNG
• Entrained Flow (oxygen-blown)
• CFB: Circulating Fluidized Bed (oxygen-blown)
• MILENA: Indirect Fluidized bed
53%
64%
70%
50%
60%
70%
Entrained Flow CFB MILENA
eff
icie
ncy
C. M
. van d
er
Meijd
en e
t.al., B
iom
ass
an
d B
ioe
ne
rgy 3
4, pp 3
02
-311
, 2
01
0.
CIRCULATING FLUIDIZED BED carbon conversion of CFB gasifier plants (2002 study)
Car
bo
n C
on
vers
ion
[%
]
Not only ~10% energy is lost, but also it poses a waste and safety issue
TAR defined as hydrocarbons larger than benzene
0 100 200 300 400 g/mol
Hydrocarbons
Tar (larger than benzene)
PAH (Poly-Aromatic-Hydrocarbons)
gasoline jet fuel diesel
Causing dew point >200°C
CH0.8O0.01N0.0001 …
TAR larger molecules = lower content
100
1 000
10 000
100 000
1 000 000
0 100 200 300hydro
carb
on c
oncentr
ation [m
g/N
m3]
hydrocarbon molecular weight [g/mol] per interval of 50
waste - indirect gasifier - 804C
wood - indirect gasifier - 820C
waste - CFB - 820C
wood - CFB - 840C
But also: if you want methane, you will have to deal with tars
TARS EVALUATION e.g. evaluate effect of gasifier temperature
TARS EVALUATION condensation behavior on “cold” surfaces
0
1
10
100
1 000
10 000
100 200 300 400 500 600 700
tar
that
co
nd
ense
s [
mg
/Nm
3]
temperature [degC]
819°C
775°C
735°C
861°C
COMPOSITION NOT CONSTANT during operation the bed material (olivine) “activates”
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5
10
15
20
25
30
35
40
0 24 48 72 96 120
Co
nce
ntr
atio
n in
dry
gas
[vo
l%]
Time on stream [hour]
MIL_CH4_P
MIL_CO_P
MIL_CO2_P
MIL_H2_P
CO2
H2
CO
CH4
Ind
irec
t fl
uid
ized
bed
ga
sifi
cati
on
(M
ILEN
A)
of
wo
od
~8
00
°C
BED MATERIAL ACTIVATION caused by migration of Fe to the surface
TAR REMOVAL
• Catalytic conversion
• Plasma conversion
• Scrubbing with water
• Scrubbing with biodiesel
• Scrubbing with another liquid
- Ideal in sense that it removes tar before cooling - Sensitive to poisons like S (limits fuel flexibility) - Inevitable also destroys part (~30%) of methane
- Simple from operational point-of-view - Consumes power (~1/3 of what is being produced)
- Tar dew point is water temperature - Produces nasty mixture of tar, particles, water
- Applied in Austrian indirect gasifier plants - Consumption biodiesel (~1 kg biodiesel/kg tar) - Only works when little tar (filter upstream and
acceptable biodiesel consumption)
- Example: OLGA
POTASSIUM (K)
Good:
• Acts as catalyst for conversion and tar reduction, allows lower temperature
• Responsible for bed material activation
Bad:
• Danger of agglomeration/melting in gasifier
• Downstream fouling by condensation of volatile salts
AGGLOMERATION
• Lower temperature
• Prevent hot spots
• Add K-getter (clay material)
• Add more surface and blow away
WHAT CHICKEN MANURE CAN DO the good thing about Potassium
0
2
4
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10
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14
840°Cwood
840°Cwood +
20% chicken manure
760°Cchicken manure
Tar
conte
nt [g
/Nm
3]
WHEN GOING CHEMICAL… sulphur removal is not just removing H2S
• Sulphur has many forms (numbers for clean wood in N2-free gas): – H2S 200 ppmv
– COS 20 ppmv
– Mercaptans 5 ppmv
– Thiophene 10 ppmv
– Benzothiophene 3 ppmv
– Dibenzothiophene 1 ppmv
• Activated carbon can remove this, but: – It will also absorb BTX and thus soon is saturated/needs regeneration
• HDS (HydroDeSulphurization) will convert the organic S, but: – Olefins will hydrogenate too (e.g. ethylene to ethane), exothermic
– Water Gas Shift reaction will occur too, exothermic
– So, temperature control is challenge
WHEN GOING CHEMICAL… hydrocarbons is more than tar and methane
• Significant amounts of olefins (mainly ethylene) and single aromatics (BTX)
• Known for their coke forming tendency
• Also: benzene emissions from engine exceed limits (e.g. Germany)
• BTX: – Can be reformed, but needs upstream S-removal to protect reformer catalyst, and
upstream activated carbon does not make sense since it absorbs the BTX
– Can be separated and used/sold, enables downstream activated carbon S-removal
• Ethylene: – Can be converted to ethane, which is much easier to handle for catalysts
– Can be converted into aromatics, and separated
– Can be separated
GREEN GAS (bioSNG)
our process choices
Smart combination of endothermal reforming and exothermal methanation
MILENA – OLGA – ESME
ECN process for biomass-to-bioSNG
Gasifier Tar
removal Up-grading
Metha-nation
CO2 removal
S removal
HDS Pre-
reformer Metha-nation Metha-
nation
Gasifier: Fluidized Bed Gasifier operating at temperature below 1000°C HDS: HydroDeSulphurization (converting organic S molecules into H2S) BTX: Benzene, Toluene, Xylene (~90%/9%/1% in case of fluidized bed gasification at ~800°C)
BTX is converted
Needed to protect reformer catalyst
Little organic-S, but too much for reformer
Ni catalyst is not able to treat BTX
<10 bar to prevent removal of methane
Prevents BTX to contaminate CO2
CO2 co-product is clean Starting point: existing catalyst and technology
MILENA OLGA ESME
MILENA – OLGA – ESME ECN process for biomass-to-bioSNG
MILENA gasifier OLGA tar removal HDS reactor Further gas
cleaning Methanation
reactors 1 bar 1 bar 6 bar 6 bar 6 bar
70% efficiency from wood to bioSNG
bioSNG PROCESS with BTX removal
Gasifier Tar
removal Up-grading
Metha-nation
Hydro-genation
BTX Metha-nation Metha-
nation
Gasifier: Fluidized Bed Gasifier operating at temperature below 1000°C BTX: Benzene, Toluene, Xylene (~90%/9%/1% in case of fluidized bed gasification at ~800°C)
S and CO2 removal
BTX removal also removes organic-S
Mainly ethylene to ethane, COS to H2S
Activated carbon guard bed is possible now
H2S and CO2 removal in one unit
No HDS required No reformer required
Starting point: existing catalyst and technology
MILENA OLGA
BTX SCRUBBER
• Removes BTX (Benzene, Toluene, Xylenes)
• Scrubbing process
• Produces liquid BTX for further use
BTX scrubber, 2 nm3/h
CONCLUDING REMARKS
• Biomass gasification has many options to make renewable energy
• And it can make money
• Main challenges: – Feeding
– Tar
– Non-conventional gas cleaning
• Fortunately, these challenges all have good solutions
• Main challenges remaining are … non-technical
CHEMICAL INDUSTRY as role model, but…
What do you get if you ask an experienced EPC in petro-chemistry to design a bioSNG plant?
What do you get if you ask an experienced car manufacturer to build a human-powered two-wheel car? Also called a bicycle.
It certainly works, but may not be the best choice
MORE INFORMATION
publications: www.ecn.nl/publications
fuel composition database: www.phyllis.nl
tar dew point calculator: www.thersites.nl
IEA bioenergy/gasification: www.ieatask33.org
Milena indirect gasifier: www.milenatechnology.com
OLGA: www.olgatechnology.com / www.renewableenergy.nl
SNG: www.bioSNG.com /www.bioCNG.com
Bram van der Drift
ECN
Westerduinweg 3 P.O. Box 1
1755 LE Petten 1755 ZG Petten
The Netherlands The Netherlands
T +31 224 56 45 15 [email protected]
M +31 610 909 927 www.ecn.nl
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